In the process of building a garage addition that has living space above. There is a single bathroom on the second story with a lav, toilet and shower. The bathoom is 12' long with the toilet and shower on opposite ends. The main stack will pass up through the wall next to the shower.
Just getting ready to start my rough in and wanted to run my dmv diagram past everyone here. My main questions are:

1. First off, does this diagram look correct or am I way off?
2. There is a utility sink on the first floor, I know I can't vent it using the bathroom lav drain but can it connect to the lav vent in the attic? And can that vent tie back into the main stack or does it need its own roof penetration? In my drawing I have it going up through the roof.
3. My toilet is roughly 12' from the main stack so I've added a vent. Would a 2" vent be sufficient for the toilet?

Under IPC, you can run an unlimited distance between the toilet and it's vent, no more 10' limitations. Also under IPC, that vent coming off of the toilet running flat is not allowed. Minimum vent size is 1/2 of the largest drain served, which in your case could be as small as a 3" drain, so 1 1'2" vent. Yes, you can revent the lower fixture vent into the bathroom vent in the attic, and yes, you can revent that vent into the main vent for the house.

REall phish ? unlimited distance ?? that seems odd zas it would make a double S trap after the 3" line exceeded 12' of distance at grade of 1/4 per foot.

our code in canada we need to have a vent ( usually the lav As a wet vent ) the tub must also come off of this wet vent ( 2" to the lav with a 2 x 1 1/2 for the tub ) or be individually vented.

Yes, really.

Think about it, the very design intent of the toilet is to FORCE it to siphon it's own trap when flushing, and then the trap is refilled by the fill valve. And now consider that the only reason for the trap to be within a certain distance of it's vent is to stop it from siphoning itself, and you can see why that code change was made.